Publication

Publication

The beam quality conversion factor, kQ, can be calculated directly using Monte Carlo simulations. In order to validate the use of these calculated values, an evaluation of the associated systematic uncertainties is required. In a Monte Carlo simulation, the relative statistical uncertainty can be reduced by increasing the number of histories at the expense of computing time. Other sources of uncertainty that must be considered originate from possible variations in photon cross‐sections, stopping powers, chamber dimensions, the choice of source use for the simulation and variation of W/e with beam energy. In this study, these systematic uncertainties are quantified with Monte Carlo calculations using different methods with the EGSnrc code system. In most cases, it is possible to assign an uncertainty on a given quantity (e.g. photon cross‐sections) based on information from the literature. The specific parameter is changed by one standard deviation and the change in kQ, ΔkQ, is calculated separately for each parameter, yielding an uncertainty in kQ from each source of uncertainty. The overall uncertainty in kQ is determined using well‐known methods. Uncertainty due to the variation of photon cross‐sections depends on whether or not the cross‐section uncertainties are correlated. If correlated the total systematic uncertainty in kQ amounts to 0.64%, or 1.0% if one assumes uncorrelated photon cross‐sections. The uncertainty in W/e (0.5%) is a major source of uncertainty which also affects all other calculations of kQ.